Field of the Invention
The present invention relates to what is called an EFEM (Equipment front end module) system used to transfer wafers held in a closed transportation container called a pod to a semiconductor processing apparatus in semiconductor manufacturing process or the like and to a lid opening/closing system using such an EFEM system.
Description of the Related Art
In semiconductor manufacturing processes in recent years, there have been widely used a method of keeping a highly clean condition only in the interior of three spaces including the interior of processing apparatuses, the interior of pods in which wafers are stored to allow transfer of the wafers between processing apparatuses, and a mini-environment (or small space) through which the wafers are transferred between a pod and each processing apparatus, thereby controlling the cleanliness throughout the process. The pod as such is a container composed of a body in which wafers are stored and that has an opening provided on one side thereof through which wafers are brought into/out of it, and a lid for closing the opening to seal the interior space of the pod. The mini-environment has an opening portion that can be opposed to the opening of the pod and a second opening portion provided on the semiconductor processing apparatus side opposite to the opening portion.
The mini-environment is supplied with clean air, which is ambient air cleaned using a filter. An apparatus used to open and close the lid of the aforementioned pod, the mini-environment, and a wafer transfer system provided in the mini-environment are collectively called an EFEM system. In the EFEM system, the cleanness of the mini-environment is kept to a predetermined level by the use of clean air supplied through the filter. With miniaturization and improvement in the performance of semiconductor devices in recent years, wiring patterns used in semiconductor devices have become finer, and it is required more strictly to prevent the patterns from being affected by oxidation.
To meet this requirement, Japanese Patent Application Laid-Open No. 2004-311940 discloses a technique in which contaminants are removed from clean gas introduced into a substrate transfer chamber constituting the aforementioned mini-environment, and the clean gas is used in a circulative manner. On the other hand, there is another attempt in which the amount of particles and oxygen concentration in the pod are reduced by what is called bottom purge introducing clean gas directly from the bottom of the pod, as disclosed in Japanese Patent Application Laid-Open No. 2007-227619.
Air (atmospheric air) cleaned using a fan filter unit (FFU) is introduced into the aforementioned mini-environment. The clean air has an oxygen concentration and a humidity higher than those of inert gas directly supplied into the pod by bottom purge in typical cases. In the case where the aforementioned supply of inert gas by bottom purge and the supply of clean gas into the mini-environment are performed at the same time, there is a possibility that the clean gas supplied into the mini-environment may enter the pod or container to be mixed with the inert gas supplied by bottom purge. Since the volume of the mini-environment is much larger than the volume of the container, even if the oxygen concentration of the clean gas introduced into the mini-environment is controlled, the oxygen concentration of the clean gas is higher than that of the inert gas introduced into the container. In consequence, the entrance of the clean gas in the mini-environment into the container may prevent satisfactory reduction of oxygen concentration inside the container by the supply of inert gas, and oxidation of the wafer surface cannot be prevented sufficiently, in some cases.